1. Field of the Invention
This invention relates generally to small, inexpensive electrical connectors; and more particularly to high-manufacturing-volume half connectors which mate with other half connectors and contact pins that are of relatively rough construction. Such rough-construction pins are particularly favorable for making ballast connections in fluorescent. luminaires.
Thus the invention is particularly useful in a half connector that is to be installed in such a ballast, or in the mating half connector in the luminaire--whichever is the connector that carries the female contact or contacts. (In this document generally we use the words "contact" and "terminal" interchangeably; these words encompass both a male pin and a female receptacle for receiving such a pin.)
2. Prior Art
For economy the electrical half-connectors used to make ballast connections in some fluorescent luminaires, and doubtless in other applications as well, employ bared wire tips as inexpensive contact pins. Such pins often are well-controlled in position and tip shape than more-expensive pins.
Accordingly the positioning--in particular the centering within its half-connector cavity--of a female contact that mates with the bare-wire or other roughly formed pin more critical than ordinarily. The positioning uncertainty due to the relatively rough nature of the male pins adds to other sources of mismate, such as warpage of the parts, and the manufacturing tolerances inherent in inexpensive construction of both half-connector bodies, and improper or angular insertion in final assembly.
The resulting misalignment of the male and female contacts is very undesirable. In such a manufacturing environment the normal design precautions to avoid misalignment include, for example, increasing the pin-support length in the mating half connector, providing a bell-mouth lead-in segment to guide the pins into the female contacts, and tightening tolerances to the extent economically acceptable. Despite all such design efforts, misalignments still occur in final assembly.
Such misalignments at assembly time constitute a problematic source of hidden extra costs. In addition to the evident annoyance and delay at the assembly line, an unknown fraction of such misalignment problems can cause concealed damage to the contacts, most typically to the more fragile female contact.
As will be understood, such damage is likely to manifest itself later in assemblies which fail after latent defects are developed during shipment. For instance, failure can occult upon installation in a laboratory, home, etc.--or even after installation.
All such results are disproportionately expensive, taking into account the cost of physical replacement and paperwork processing, as well as the wasted cost of initial shipment, installation, and removal. For all these reasons, avoiding misalignment at the outset is highly desirable.
Some contacts are inherently centered within their respective through-holes in half-connector bodies, by virtue of close transverse spacing (in circular holes, this is radial spacing) between the contact and the interior wall of the through-hole. Such close spacing, however, requires use of relatively expensive contacts or relatively expensive half-connector molding shapes, or relatively expensive assembly procedures, or combinations of these undesirable features.
This is so because common contact designs incorporate laterally outward-springing tangs, or other retaining elements, to retain each connector in its hole. The use of close spacing is inconsistent--in terms of overall economy--with the need to leave a space inside each through-hole for expansion of the tangs or operation of other retaining elements.
For instance one terminal or contact that is on the market is square, and is for use in a square through-hole--except where transverse clearance is to be provided for expansion of metal tangs. Those tangs spring out laterally from sides of the contact to engage the interior of the through-hole, to retain the contact in the hole.
This type of contact requires additional operator attention and very slight additional time to orient each connector rotationally relative to its hole. The fractional seconds consumed in this effort, multiplied by many millions of pins, amount to unacceptable added cost.
One solution to this problem might be sought in the form of a separately formed centering ring or ferrule inserted into the hole at the forward end--in other words, the end that mates with the other half connector. The additional cost, however, of separately forming and assembling such a ferrule would be undesirable.
Accordingly it can be seen that many seemingly natural solutions to the problem posed here are foreclosed, or at least rendered economically adverse, by the extremely stringent cost considerations imposed by the high-manufacturing-volume, low-product-cost environment that has been described.
Some additional candidate solutions, which will be discussed in the following section of this document, are rendered relatively problematic by still other constraints that arise from the physical nature of the production process. In particular, connector bodies are most economically made by molding from plastic, and it is well understood that plastics molding imposes its own restraints upon a designer's freedom to give the inside of each through-hole a desired shape.
In particular, as is well known, molded parts with holes require provision, in the mold, of a pin corresponding to each desired hole--and each pin must be removable from the finished, molded part. The removal of each mold pin must be accomplished either by motion in the same direction in which the mold is parted (so that it can be performed as part of the same mechanical operation as parting of the mold), or in a different direction (and separate operation) from parting of the mold.
This fundamental characteristic of the molding process, combined with the relative costliness of employing pins that must be removed as a separate operation, militates against designing so-called "undercut" features into a molded part. By "undercut" we refer to any internal space that is relatively large in comparison with a relatively small opening nearer to the surface of the part--in the direction in which the main pins will be removed.
Providing the additional transverse pins needed to make undercut features, and the added time and effort required for insertion and withdrawal of those pins in each molding cycle, is sometimes called, in the molding industry, "double pull" molding. Double-pull operation is unacceptable or at least highly undesirable in the context of high-production-volume, low-price industrial items such as ballast and luminaire connectors.
This becomes particularly clear when the resulting potential for additional operating interruptions during each production run is taken into consideration. Therefore a "single pull" molding operation is extremely desirable for purposes of maintaining manufacturing throughput and economy; and as will be seen double-pull operations are unavoidably associated with some additional otherwise-inviting solutions to the situation discussed above.
As can now be seen, the prior art has failed to provide solutions to important problems of economy and efficiency in the manufacturing of certain kinds of connectors--particularly those employing relatively rough-construction male pins. These problems are especially significant in the fluorescent-luminaire industry.